1. Technical Field
The present invention relates to a magnetic head suitable for perpendicular magnetic recording, a process of manufacturing the magnetic head, and a magnetic disc apparatus mounting the magnetic head.
2. Background Art
In magnetic disc apparatuses, data on a recording medium is read and written using a magnetic head. In order to increase the recording volume per unit area on a magnetic disc, areal density must be increased. In the current longitudinal recording systems, however, as the length of bits that are recorded decreases, the areal density cannot be increased due to thermal fluctuations in the magnetization in the medium. To solve this problem, a perpendicular recording system has been proposed whereby a magnetization signal is recorded in a direction perpendicular to the medium.
There are two types of perpendicular magnetic recording. One employs a double-layer perpendicular magnetic recording medium comprising a soft underlayer, and the other employs a single-layer perpendicular medium having no underlayer. When a double-layer perpendicular magnetic recording medium is used as the recording medium, recording must be carried out using a so-called single pole type (SPT) head having a main pole and an auxiliary pole, so that a larger intensity of magnetic field can be applied to the medium.
In addition to the strength of the head field for recording, the magnetic field gradient in the perpendicular component of the head field with which the transition width of the recording bit cells is determined, namely the field gradient in the head-field perpendicular component in the direction of head transport, is a very important factor for realizing high recording density. In order to achieve ever-higher recording density in the future, the field gradient must be further increased. Also, the curvature of the magnetic-transition pattern in the recording bit cells poses an obstacle for the realization of higher recording densities.
In order to improve recording density, track density and linear density must be increased also in perpendicular recording. For obtaining an improved track density, the track width of the magnetic head must be made finer and more precise. When perpendicular magnetic recording is carried out on a double-layer perpendicular magnetic recording medium using a SPT head, the distribution of the recording magnetic field generated by the poles in the SPT head differs greatly from that obtained in the case of using a thin-film inductive head for longitudinal magnetic recording. Specifically, the distribution is such that the contour lines of the head recording field strength are distributed concentrically, with the center portion of the main pole exhibiting a maximum strength and the contour lines getting wider and wider between adjacent lines towards the outside. As a result, the magnetic-transition pattern that is recorded is curved such that the magnetic-transition position in the track center portion is located towards the disc rotation direction more than the magnetic-transition pattern in the track edge portion. Such a phenomena has been actually clearly identified based on the result of observation by magnetic force microscopy (MFM).
The aforementioned phenomenon is produced by the fact that the main pole is made of only one magnetic layer. A magnetic head is known in which a shield made of a magnetic material is provided near the main pole of the magnetic head, such as ones disclosed in Patent Document 1 and Non-patent Documents 1 to 6, which are listed below. The techniques disclosed in these documents are designed in light of the increase in magnetic field gradient and are not intended for correcting the problem of curvature of the magnetic-transition pattern in the recording bit cells. While Patent Documents 2 discloses a structure in which the auxiliary pole is provided with a protruding portion, this protruding portion is different from the aforementioned shield, which draws the magnetic field. The protruding portion is also displaced away from the main pole by a distance of several microns, so that it cannot provide the effect provided by the present invention, as will be described below.
(Patent Document 1)
U.S. Pat. No. 4,656,546
(Patent Document 2)
JP Patent Publication (Kokai) No. 2002-92820 A
(Non-patent Document 1)
IEEE Transactions on Magnetics, Vol. 38, No. 4, pp.1719–1724 (2002)
(Non-patent Document 2)
IEEE Transactions on Magnetics, Vol. 38, No. 1, pp.163–168 (2002)
(Non-patent Document 3)
Technical Report of the Institute of Electronics, Information and Communication Engineers, MR2001-87, pp.21–26
(Non-patent Document 4)
Technical Report of the Institute of Electronics, Information and Communication Engineers, MR2002-65, pp.1–6
(Non-patent Document 5)
Abstract No. FA02 of the 47th Annual Conference on Magnetism and Magnetic Materials
(Non-patent Document 6)
Abstract No. FA03 of the 47th Annual Conference on Magnetism and Magnetic Materials